U.S. patent number 5,635,093 [Application Number 08/597,378] was granted by the patent office on 1997-06-03 for heating plate for heating an object placed on its surface and chemical treatment reactor equipped with said plate.
This patent grant is currently assigned to Commissariat A L'Energie Atomique. Invention is credited to Chantal Arena, Patrice Noel.
United States Patent |
5,635,093 |
Arena , et al. |
June 3, 1997 |
Heating plate for heating an object placed on its surface and
chemical treatment reactor equipped with said plate
Abstract
A heating floor or plate for heating an object such as a
substrate placed on its surface. A plate is provided whose surface
temperature can be accurately adjusted so that the heat quantity
supplied by two surface zones of the plate can be different even if
the zones are small and contiguous. The plate has n zones, each
having placed therein an electrically conducting heating element.
n+1 sensors are used to measure the temperature of the plate, where
n is an integer greater than 1. Data output from the sensors is
processed and compared with at least one reference value and the
result used to regulate the intensity of the current flowing in the
elements based on the comparison.
Inventors: |
Arena; Chantal (Le Fontanil,
FR), Noel; Patrice (Sassenage, FR) |
Assignee: |
Commissariat A L'Energie
Atomique (Paris Cedex, FR)
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Family
ID: |
9417659 |
Appl.
No.: |
08/597,378 |
Filed: |
February 8, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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211313 |
May 27, 1994 |
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Foreign Application Priority Data
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Oct 7, 1991 [FR] |
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91 12315 |
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Current U.S.
Class: |
219/444.1;
118/725; 219/448.12; 219/448.17 |
Current CPC
Class: |
H05B
3/68 (20130101); G05D 23/1932 (20130101); G05D
23/1934 (20130101); G05D 23/22 (20130101); H05B
2213/07 (20130101) |
Current International
Class: |
G05D
23/22 (20060101); G05D 23/20 (20060101); H05B
3/68 (20060101); H05B 003/68 (); C23C 016/00 () |
Field of
Search: |
;219/464,465,466,448,459,452 ;118/724,725,50.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Walberg; Teresa J.
Assistant Examiner: Paik; Sam
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Parent Case Text
This is a continuation of application Ser. No. 08/211,313 filed on
May 27, 1994, now abandoned, which was filed in PCT Application
Number PCT/FR92/00926 filed on Oct. 6, 1992, published as
WO93/07550, Apr. 15, 1993.
Claims
We claim:
1. A heating plate for heating an object such as a substrate placed
on its surface, said plate comprising:
a bed plate made from a material having good thermal conductivity,
said bed plate having n zones, where n is an integer greater than
1;
a plurality of electrically conducting elements of length L.sub.n,
with one of said elements being placed in each zone, each element
being traversed by a current of intensity I.sub.n to heat the
corresponding zone;
n+1 sensors, each measuring the temperature of the surface of the
bed plate and being positioned at ends of each zone;
means for processing pairs of data supplied by the measuring
sensors at either end of a corresponding zone to be heated;
means for comparing a value supplied by the means for processing
with at least one reference value; and
means for regulating the intensity of the current flowing in each
element, depending on the output of the comparison means, to adjust
independently the heat quantity supplied by each zone in order to
obtain a chosen temperature profile.
2. A heating plate according to claim 1, wherein the bed plate is
circular and the zones are annular and concentric.
3. A heating plate according to claim 1 or 2, wherein each
conductor element is positioned within the corresponding zone in
the form of a spiral.
4. A heating plate according to claim 3, wherein the bed plate is
internally provided with a spiral groove within which is brazed the
corresponding element.
5. A heating plate according to claim 1, wherein the sensors are
thermocouples.
6. A heating plate according to claim 1, wherein the means for
processing receives data from two measuring sensors on opposite
ends of a zone to be heated and calculates the mean value
thereof.
7. A heating plate according to claim 6, wherein the means for
comparing compares the mean value with a reference temperature.
8. A heating plate according to claim 1, wherein the regulating
means includes n variable current supply means, with each current
supply means being connected to two ends of an element.
9. A reactor for the chemical treatment of a substrate, comprising
the heating plate according to one of claims 1, 2, 5, 6, 7 or 8,
said plate receiving said substrate on its surface.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heating floor or sole for
heating an object, such as a substrate, which is preferably thin
and placed on its surface, as well as to a chemical treatment
reactor having such a sole.
2. Discussion of the Background
Chemical treatment reactors more particularly make it possible to
produce deposits of materials, e.g. by the procedure known as
chemical vapour deposition or CVD, on a substrate. Said substrate
is generally a silicon wafer used in the manufacture of electronic
components. This type of chemical treatment requires the substrate
to be heated to between 20.degree. and 1000.degree. C.
Chemical treatment reactors are able to heat the substrate either
indirectly by radiation emitted by a light source such as tungsten
halogen lamps (cf. in particular the reactor of the Spectrum
Company), or directly by contact between said substrate and a
heating plate (cf. in particular the reactor of the Varian
Company). In the case where the substrate is placed on a heating
plate, the temperature distribution at the substrate directly
corresponds to the temperature distribution on the plate.
However, in reactors, said substrate is sometimes kept in contact
with the plate by a peripheral clamping ring, which exerts a
pressure on the periphery of said substrate. As said ring is
generally a good heat conductor, locally there is frequently a
temperature drop in the substrate.
Moreover, in the prior art plates, the metal bed or base plate
thereof only contains a single heating resistor positioned in
accordance with a particular spatial distribution, which is adapted
to its use. As this heating resistor is traversed by a single
current, the only possible temperature variations on the surface of
the plate are due to surface distribution differences of the
heating resistor in the bed plate. It is therefore difficult for
steric dimensional reasons to overheat a precise zone in order to
make up for a local temperature drop.
U.S. Pat. No. 3,134,006 discloses a temperature checking system for
a heating element having sensors and control loops of the master
and slave type. EP-A-165 114 discloses a heat regulating device for
a hot runner mould. However, the teachings of these documents are
not applicable to a heating plate.
It would therefore be desirable to have a heating plate whose
surface temperature can be more accurately adjusted and whereof the
heat quantity supplied by the two surface zones of the plate can
differ even if said zones are small and contiguous.
SUMMARY OF THE INVENTION
To this end, the invention relates to a heating plate for ensuring
the heating of an object placed on its surface, said plate
incorporating a bed or base plate made from a material having a
good thermal conductivity.
According to the features of the invention, the bed plate comprises
n zones, within each of which is placed an electricity conducting
element of length L.sub.n, traversed by a current of intensity
I.sub.n and intended for ensuring the heating of the corresponding
bed plate zone, n+1 sensors for measuring the temperature of the
surface of the bed plate, said measuring sensors being positioned
at the ends of each zone, n being an integer greater than 1, means
for the pairwise processing of data supplied by the measuring
sensors surrounding the corresponding zone to be heated, means for
comparing the value supplied by the processing means with at least
one reference value and means for regulating the intensity of the
current I.sub.n flowing in each electricity conducting element,
said regulating means being dependent on the comparison means.
Thus, as a result of the invention, it is possible to subdivide the
heating plate surface into several zones to be heated. The number
of zones will be determined as a function of the heating accuracy
which it is desired to obtain. Two temperature measuring sensors
are associated with each zone to be heated. The values measured by
these sensors are transmitted to the processing means, which supply
a calculated value. The latter is then compared with a reference
value corresponding to the desired temperature in said zone. This
reference value can be the same or different for all the zones.
When said reference value is unique, the temperature profile of the
bed plate is flat. However, when the reference values differ, there
is a different temperature profile, e.g. a curve rising from the
centre of the bed plate. Moreover, even in order to maintain a flat
temperature profile, bearing in mind local heat losses, two
contiguous zones can receive different heat quantities by means of
the conductor elements. Thus, these conductor elements can have a
different surface distribution and length L.sub.n. As a result of
the regulating means, is also possible to differently vary the
intensity of the currents I.sub.n flowing through said conductor
elements.
Preferably, the bed plate is circular and the different bed plate
zones are annular and concentric.
To the extent that the treated objects, such as the substrates are
generally circular, because they are usually silicon wafers, the
circular shape of the bed plate and the concentric shapes of the
heating zones are particularly appropriate for this type of
application. However, it is obvious that for objects having
different shapes, it would be possible to envisage other shapes of
the bed plate or the zones without passing outside the scope of the
invention.
Advantageously, the conductor element is positioned within each
zone in accordance with a spiral. This particular arrangement is
advantageous because, when the conductor element is particularly
rigid, there is an avoidance of bent lines, which could lead to the
breaking of said element.
Preferably, the temperature measuring sensors respectively
incorporate a thermocouple, which is readily commercially
available. However, it would also be possible to use other
temperature measuring sensors such as e.g. optical pyrometers
positioned outside the bed plate.
Advantageously, the data processing means supplied by the two
measuring sensors surrounding a zone to be heated make it possible
to calculate the mean value of the two temperatures supplied. It
would also be possible to envisage performing another calculation
on the basis of the two temperatures supplied by the measuring
sensors. This calculation is dependent on the desired temperature
profile on the bed plate.
Finally, the regulating means incorporate n variable current supply
means, each of them being connected to the two ends of one of the
electricity conducting elements. These means can be easily produced
and are inexpensive. As a function of the variations between the
calculated value and the reference value, the regulating means,
dependent on the comparison means, react so as to vary the
intensity of the current at the terminals of each conductor
element.
The invention also relates to a reactor for the chemical treatment
of a thin substrate having a heating plate like that described
hereinbefore and which is intended to receive on its surface the
said substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described in greater detail hereinafter relative
to a preferred embodiment and with reference to the attached
drawings, wherein show:
FIG. 1 A diagram of the invention, the plate being shown from
above.
FIG. 2 A sectional view of the heating plate according to the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
For great clarity of the description, a substrate will be used as
the example of the object placed on the heating floor or plate.
As illustrated in FIG. 2, the heating plate according to the
invention is to be used for heating a not shown substrate placed on
its surface 2. The plate comprises a bed or base plate 4 made from
a material having a good thermal conductivity. This material must
also have a good mechanical behaviour compatible with the
temperature of use. For example, it is possible to use certain
metals, boron nitride or graphite.
This bed plate 4 is internally provided with a preferably
continuous groove 6 having a planar spiral shape and within which
are placed and brazed n conductor elements 8, n being an integer
greater than 1. These conductor elements 8 are only
diagrammatically shown in FIG. 1.
In the preferred embodiment of the invention, the bed plate 4 of
the heating plate is circular, because the treated substrate is
also circular. Therefore the conductor elements 8 are preferably
arranged in spirally wound manner along the groove 6. The n
electricity conducting elements 8 in each case have a variable
length L.sub.n. Each electricity conductor 8 defines at the surface
of the bed plate 4 a corresponding zone 10. More specifically, each
zone is defined by the dimensions and the winding of a conductor
element 8. Consequently, as a function of the length L.sub.n of the
conductor element and its surface distribution, the zone 10 will be
of varying width. The zones 10 are annular and concentric.
The heating plate also has n+1 temperature measuring sensors 12,
which are preferably arranged substantially level with the two ends
of each electricity conductor element 8. In other words, each
measuring sensor 12 is placed between the ends of two adjacent
windings of elements 8. These sensors are preferably thermocouples.
Consequently and as can be seen in FIG. 1, it is also possible to
consider that a thermocouple is positioned on the one hand on the
inner, annular rim of a zone 10 and that the following thermocouple
is placed on the outer rim of said same zone. These thermocouples
are of a conventional nature and will consequently not be described
in greater detail. As illustrated in FIG. 2, they make it possible
to record the temperature at a point 13 on the surface 2 of the bed
plate 4 above said thermocouple 12.
As can be seen in FIG. 1, the heating plate according to the
invention incorporates means 14 for processing the data supplied by
the measuring sensors 12. These processing means 14 comprise a
computer making it possible to pairwise process the data supplied
by the two measuring sensors 12 located at the two ends of the same
zone 10. The processing means 14 e.g. make it possible to form the
mean value of two temperatures recorded on two sides of the zone 10
and deduce therefrom the mean temperature prevailing at the level
of the surface of the plate in said zone.
The plate also incorporates comparison means 16 connected to the
data processing means 14 and making it possible to compare the
value supplied and calculated by the processing means 14 with a
reference value 18 corresponding to the treated zone. The
comparison means 16 are connected to means for regulating the
intensity of the current I.sub.n flowing in each conductor element
8, said means being given the general reference 20. These
regulating means 20 comprise n variable current supply means 22,
whereof only one is diagrammatically shown in FIG. 1. Each means 22
is connected to the two ends of a conductor element 8.
The present invention makes it possible to produce a plate where
the heating temperatures can be adjusted during its manufacture
and/or during its operation.
During manufacture, the length L.sub.n of each conductor element 8
can be adjusted so as to have a surface distribution corresponding
to the heat quantity which it is wished to obtain in a given zone.
The length L.sub.n of each conductor element 8 is also conditioned
by the plate dimensions.
During operation, the supply means 22 make it possible to vary the
intensities injected into the conductor elements 8, which also has
the effect of varying the temperature on the corresponding surface
2 of the bed plate 4.
Finally, the number of each conductor element 8 will be determined
as a function of the precision of the temperature profile required
on the surface of the bed plate 4.
The plate according to the invention is more particularly intended
for use in a chemical treatment reactor, but it could also be used
for other purposes where a precise heating of an object is
necessary.
* * * * *